[$] Subinterpreter support for Python

Eric Snow kicked off the 2018 edition ofthe Python Language Summit with a look at getting a better story formulticore Python by way of subinterpreters. Back in 2015, we looked at his efforts at that point; thingshave been progressing since. There is more to do, of course, so he ishoping to attract more developers to work on the project.

This is the start of the Python Language Summit coverage for this year; articles are being collected on a dedicated summit page as they are finished.